Private Branch Exchanges (PBX's) have increased in complexity and sophistication over the years and offer users a wide variety of features and capabilities that are activated by a user from multi-function station sets. Multi-function station sets typically have multiple call appearances which allow the user to have multiple active concurrent independent call connections. The user, however, can only talk on one call connection at a time. To maintain multiple active call connections, the user activates a "hold feature" to keep the remaining call connections active but in a "non-talk" state. The user can maintain several calls "on-hold" while conversing with another party or parties (e.g. conference connections). Although the hold feature is convenient to the user or activating party, the held party must aurally monitor the station's receiver for the return of the voice of the activating party to ascertain the conclusion of the hold interval and the re-establishment of the "talk" state. The held party, as a result of aural monitoring during the hold interval, suffers a number of inconveniences such as waiting an uncomfortably long period of time, wasting valuable time, and enduring restricted activity.
Many systems and devices have been proposed in an effort to alleviate these inconveniences to the held party. One such device applies soothing music on the station line during the hold interval so as to entertain the held party. Another system measures the time duration of the hold interval, and then drops the call connection after some period of time elapses. Other arrangements provide a "winking" lamp on the station of an activating party to serve as a reminder to the activating party that an existing call connection is "on-hold". Despite the above-described attempts to alleviate the inherent annoyances to the held party, the held party must still aurally monitor the station's receiver for the entire hold interval to detect the activating party's voice which signals the resumption of the "talk" state connection between the held and activating parties.
Schemes have been proposed which eliminate the need for the held party to aurally monitor the receiver of the station set by providing an indication to the held party that signals the return of the activating party's voice and the conclusion of the hold interval. One such voice detection scheme is disclosed in U.S. Pat. No. 3,961,142 issued to George S. Caffine on Jun. 1, 1976. Caffine discloses an arrangement wherein each station is equipped with a hard-wired voice detection circuit which is activated by the held party during a hold state. The circuit monitors the held party's station line during the hold state to detect the presence of a voice signal thereon. An annunciation signal is generated by the detection circuit in response to the detection of voice on the station's line signaling the resumption of the "talk" state between the held party and the activating party. The voice detection circuit eliminates the need for the held party to aurally monitor the station's receiver.
There are several disadvantages associated with the Caffine and similar voice-detection arrangements. These arrangements typically disclose a hard-wired voice detection circuit which is dependent on the tip/ring architecture of an analog key system. This circuit detects electrical changes in the voltage applied to the tip/ring conductors and activates an annunciation signal in response to the detection of a voltage change. These voice detection arrangements are appropriate for analog environments where changes in electrical signals control the interconnections between stations; however such voice detection arrangements are inapplicable to digital environments where interconnections between stations occur in response to call processing algorithms which generate digital messages. Therefore, the application of these voice detection arrangements is limited to analog environments which are based on tip/ring architecture.
Another disadvantage of the voice detection arrangements is that the voice detection circuit links the detected changes in the electrical signals on the tip/ring conductors to the appearance of voice on the station line. Arrangements that rely on changes in electrical signals to indicate a particular condition are not reliable since changes in the electrical signals could occur as a result of noise appearing on a line. The noise could trigger the circuit and provide a false indication as to the appearance of voice on the station line. Additionally, the circuit does not discriminate the activating party's voice from other voices that can appear on the station's line. The circuit could then generate the annunciation signal in response to the "music on-hold" feature, cross-talk or the appearance of other conferees' voices on the line where a conference connection exists.
A further disadvantage associated with these voice detection arrangements is that the voice detection circuit is not triggered until a voice signal is detected and therefore, if the activating party does not immediately speak at the conclusion of the hold interval--a delay in conversation between the activating and held parties occurs. One other disadvantage of these arrangements is that physical modification to an existing station set is required to provide this feature to a user.
Therefore, there exists a need to develop a held party notification arrangement which is independent of the tip/ring architecture, operates in the digital environment and provides an immediate and "true" notification to the held party that the hold condition has been removed and the "talk" state connection has been re-established. Additionally, an arrangement is desired that requires no hardware modification and is implemented in an economical manner.